What is an Immersion Heater?

Immersion heaters are commonly found in properties across the country, suitable for both small apartments and larger homes. But what exactly are they?

In this article, we’ll take a closer look at immersion heaters, explaining how they function, their advantages and disadvantages, and how they compare to gas boilers.

First, let’s explore how immersion heaters work…

How Do Immersion Heaters Work?

Immersion heaters heat water using a metal element inside a hot water cylinder. In simple terms, it’s like a large kettle, with an electric resistance heater (a metal loop or coil) warming the surrounding water.

Typically, immersion heaters are connected to the electricity supply through a switch, allowing you to turn them on and off as needed. They can also be fitted with timers, enabling you to automate when they heat water.

Which Homes Use Immersion Heaters?

Immersion heaters are used in various homes, from small flats to larger properties with multiple bathrooms. In smaller homes that lack a gas supply, immersion heaters heat water stored in a hot water cylinder using the mains electricity.

In larger properties with higher demand for hot water, immersion heaters can serve as a backup if your boiler breaks down.

Additionally, immersion heaters are commonly used in homes with non-traditional heating systems, such as heat pumps, making them a good solution for heating water in those setups.

Are Immersion Heaters Energy-Efficient?

Since immersion heaters run solely on electricity and do not use gas, they produce no exhaust fumes during the heating process. This makes them more energy-efficient than traditional gas boilers.

You can also install timers and thermostatic controls on your immersion heater. These features help reduce energy waste by heating only the water you need and giving you greater control over the temperature.

Another way to improve energy efficiency is by adding an insulating ‘jacket’ to your hot water cylinder, enhancing heat retention.

However, if you’re thinking about replacing your combi boiler with an immersion heater, consider the following:

  • Combi boilers provide hot water on demand, eliminating the need to store heated water.
  • Fresh hot water from a combi boiler reduces the risk of bacteria buildup.
  • Gas is generally cheaper than electricity.

How Much Does an Immersion Heater Cost to Run?

According to research, most immersion heaters consume 3kW of electricity per hour. With the January 2024 energy price cap set at £0.29 per kWh, the cost of running an immersion heater is £0.87 per hour.

For example, a 3kW, 180-litre immersion heater running two full heating cycles per day (morning and evening) would typically take about 3 hours to heat the water. Over the course of a day, it would run for about 6 hours.

6 x £0.87 = £5.22

It’s important to note that this is an estimate, and actual costs will depend on factors like:

  • The size of the tank
  • How much water you use
  • The temperature you heat the water to
  • How well your hot water tank is insulated
  • When the heater is scheduled to run (off-peak electricity tariffs may make it cheaper to run the heater at night)
  • If you have temperature sensors to turn the heater off once the water reaches the desired temperature

Additionally, if your immersion heater is connected to a solar panel system, you may be able to heat water without relying on the National Grid, making it a more cost-effective option. However, you will need to consider the installation cost of solar panels.

How to Maximise the Efficiency of Your Immersion Heater

To ensure you always have hot water when you need it without wasting energy, you should:

  • Insulate your hot water tank to improve heat retention using foam tubing around pipes and an immersion heater blanket around the cylinder.
  • Use a thermostatic control to automatically turn off the heater once it reaches the desired temperature.
  • Set a timer to turn the heater on and off when needed. If you’re on an Economy 7 energy tariff, you can schedule the heater to operate during off-peak hours.
  • Reduce the temperature if the water is hotter than necessary (a minimum of 50ºC is required to kill bacteria).

What Are the Pros and Cons of Immersion Heaters?

If you’re considering an immersion heater, or comparing it to traditional central heating systems, it’s helpful to know the pros and cons.

Pros of Immersion Heaters:

  • Provide hot water even if your central heating boiler breaks down.
  • Insulated cylinders can keep water warm when the heater is off.
  • If you’re on an Economy 7 tariff, you can set the heater to come on during cheaper off-peak hours.
  • Can be used with renewable energy sources like solar panels.
  • Simple to operate with just an on/off switch and basic thermostat controls.

Cons of Immersion Heaters:

  • Only use electricity, which is generally more expensive than gas.
  • Must heat water to at least 50°C to eliminate bacteria.
  • Without a thermostatic control and timer, immersion heaters can be expensive to run.
  • Cannot supply radiators.
  • Do not provide hot water on demand like a combi boiler.
  • Heating small amounts of water can be time-consuming.
  • Even with insulation, water in the tank can cool down quickly.

Immersion Heaters vs Gas Boilers: Which Should You Choose?

While immersion heaters can be a useful option—especially as a backup if your central heating boiler breaks down—they are not as efficient or versatile as gas boilers. Immersion heaters work separately from the heating system, meaning they can’t heat radiators or provide hot water on demand like a combi boiler can. For many, they are a complementary solution rather than a replacement for a gas boiler.

For more information on installing or upgrading your heating system, get in touch with Advanced Plumbing and Heating today!